The invention relates to self-cooling cans, and in particular to improvements in sorption temperture changers which were prevously patented by the present inventor. The sorption temperature changers have been described in detail in U.S. Pat. No. 4,250,720 (1981). Essentially, the sorption temperature changers use the fact that the boiling temperature of water is lowered under a partial vacuum. The basic components of the temperature changers are 2 chambers consisting of a water chamber and a dessicant chamber. The water chamber contains water under a vacuum. The water boils in the water chamber at relatively low temperatures because of the partial vacuum in the chamber. This cools the surfaces of the water chamber. The cold surfaces of the water chamber then absorb heat from a beverage.
The removal of the vapors generated by the boiling water is essential for the initiation and continuation of the boiling of the water in the water chamber. This vapor removal is accomplished by a dessicant in the dessicant chamber which adsorbs or absorbs the vapors generated by the boiling water in the water chamber. The boiling of the water in the water chamber is reglulated by opening and closing the communication between the cooling chamber and the dessicant chamber. When the communication between the water and dessicant chamber is closed the boiling of the water stops. The temperature changers are inactive and can be stored for indefinite periods at environmental temperatures without losing their temperature changing potential. The temperature changing action of the device will, however, be initiated by the opening of the communication between the water and the dessicant containers.
The above disposable temperature changers suffer from the fact that their chambers require relatively strong walls to withstand the outside atmospheric pressures during the initiation of the partial vacuum in the chambers. The strong walls may be too expensive for the disposable forms of the temperature changers. The present invention provides new means whereby a vacuum can be maintained in weak wall chambers. This is achieved through porous support bodies placed between the walls of the chambers. As will be described in detail, the inner body maintains the interspaces in the cooling container, and provides an inner support for the walls of the container.
In the original patent the water chamber was adapted to serve as a wall of a beverage container. Under those conditions, one wall of the water chamber served as the inner surface of a the double walled beverage container, while the opposite wall of the water chamber served as the outer wall of the double wall beverage container. Thus, only half the surfaces of water chamber (the inner wall of the double wall beverage container) are in contact with the beverage and are available for absorbing heat from the beverage. The present invention contains a structural modification whereby the complete water chamber is immersed in the beverage. Thus, all the potential heat exchange surfaces of the chambers become available for cooling the beverage.
In one version of the present invention multiple dessicant chambers are used instead of the single dessicant chamber used in the unmodified form of the invention. Each of the multiple dessicant chamber communicates independently with the water chamber. This is based upon the fact that the most rapid cooling occurs during the initial exposure of the dessicant to the water vapor. Thus, when the communication between the water and the dessicant chamber is first established there is a vigorous boiling of the water in the cooling chamber and a rapid heat loss from the beverage. This is followed by a slower rate of evaporation, and a slower cooling of the beverage. This occurs before the dessicant becomes saturated with the vapor and is independent of the temperature of the water. The multiple dessicant chambers provide means whereby the the more rapid initial boiling of the working fluid and cooling can be repeated without increasing the total quantity of the dessicant. This is accomplished by means which allow serial exposures of the water chamber to the dessicant chambers.
A more detailed description of the above improvements. given in the Detailed Description section, will further clarify the nature of the improvements.